[33.20] Crab/Vela Winds and Pulsar model topologies

F. C. Michel, I. A. Smith (Rice Univ.)

Recent observations of the Crab and Vela by HST and Chandra
have revealed that the winds seem to form polar jets and
equatorial outflows. Features in the Crab winds flow with
velocities comparable to c, which is no surprise
theoretically. But the theoretically assumed wind patterns
typically were more or less uniform outflows (e.g., Melatos
and Melrose 1996, Fig. 1), unlike the jet/equatorial
patterning. Interestingly, however, this geometry exactly
parallels the expected distribution of trapped plasma around
an aligned rotator (Krause-Polstorff and Michel 1985):
plasma of one sign of charge is concentrated over the
magnetic polar caps while the opposite sign plasma is
concentrated in the equatorial regions. Unfortunately, it is
not obvious how the wind is formed. We have examined several
mechanisms (Smith, Thacker, and Michel 2000) and so far are
forced to conclude that inclination of the dipole is
essential and that plasma must be forced away by the
resultant large-amplitude waves in the wave zone (a.k.a.
light-cylinder). The KPM simulations showed that the popular
Goldreich-Julian (1969) model was incorrect because two
incompatible assumptions were made: (1) that the charged
particles come from the neutron star surface and (2) that
the magnetosphere is entirely filled by these particles. The
KPM simulation initially adopted only assumption (1).
Recently Contopoulos et al. (1999) found numerical solutions
adopting assumption (2). Neither solution is GJ. However,
assumption 2 would require ionization processes at
implausible distances for typical pulsars.

These results are of particular relevance to the popular
assumptions that

1. Radio emission comes from the magnetic polar caps,

2. Plasma is accelerated from the magnetic polar caps,

3. Inclination of the dipole simply rotates the beam,

4. An aligned rotator would function as an "unpulsed"
pulsar, and

5. Plasma is centrifugally ejected at the light-cylinder.

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